FIGS. 1A-B respectively illustrate plan views of a functional surface 102 and a non-functional surface 104 on opposite sides of a singulated electronic device 100. The functional surface 102 comprises electrical contacts 106 of the electronic device 100, and the non-functional surface 104 comprises a laser marking 108 and an orientation mark 110. The laser marking 108 is provided for batch traceability and the prevention of lot mixing, and the orientation mark 110 is provided as an indicator to aid in orientating the electronic device during processing.
FIG. 2 shows an apparatus for inspecting the non-functional surface 104 of the electronic device 100. A light source 120 projects a light, which is reflected by a beam splitter 122 onto the non-functional surface 104 of the electronic device 100. The non-functional surface 104 reflects the light, which travels through the beam splitter 122 and is received by an imaging device 124. Thus, the imaging device 124 captures an image of the non-functional surface 104 of the electronic device 100.
If the electronic device 100 comprises a substrate which is opaque to the light that is projected onto the electronic device 100, a clear image 126 would be captured by the imaging device 124, as shown in FIG. 3A. The laser marking 108 and the orientation mark 110 absorbs, diffracts or disperses the light projected onto them, while the rest of the opaque substrate reflects the light. Thus, a clear image 126 is formed where a laser marking image portion 128 and an orientation mark image portion 130 are contrasted by a background image portion 132.
However, if the electronic device 100 comprises a substrate which is substantially transparent to the light that is projected onto the electronic device 100, an obscured image 134 is captured by the imaging device 124, as shown in FIG. 3B. This is because the incident light is transmitted through the transparent substrate of the electronic device 100 until the light is reflected by underlying circuitry 136 (see FIG. 2) in the electronic device 100. Hence, the laser marking image portion 128 and the orientation mark image portion 130 are obscured by a circuitry image portion 138. As depicted in the obscured image 134 in FIG. 3B, the underlying circuitry 136 obscures the laser marking 108 and the orientation mark 110, thus making inspection of the laser marking 108 and the orientation mark 110 difficult and inaccurate.
In order to address the aforesaid problem, a polymeric layer which is opaque to the projected light may be applied onto the non-functional surface 104 of the electronic device 100. In this way, the incident light is reflected by the polymeric layer 140 without passing through the transparent electronic device 100, allowing a clear image 126 depicting the laser marking image portion 128 and the orientation mark image portion 130 to be captured. Since the light is not transmitted through the transparent substrate, it does not reach the underlying circuitry 136, which obscures the inspection process. However, the polymeric layer adds to the thickness of the electronic device 100, and this additional thickness is unacceptable or undesirable for certain applications. The process of adding the polymeric layer may also introduce unnecessary complexity and impurities to the manufacturing process.
Hence, it would be beneficial to seek to provide a method of inspecting substantially transparent substrates which ameliorates at least some of the aforementioned problems of the prior art.